The Euchelicerate Limuloides and Other Bunodidae from the Upper Silurian (Wenlock Přĺdolĺ) of England

Limuloides (Woodward, 1865) (Euchelicerata: Bunodidae) are marine “synziphosurans” distinguished by nine scalloped, horizontally oriented radial ridges on the dorsal prosoma and prominent spines on the prosomal margins. Material is reported from the upper Silurian of England, the vast majority coming from the Anglo-Welsh basin (Wenlock-Přídolí) plus a single specimen from the Windermere Supergroup of Cumbria (Ludlow or Přídolí); an unconfirmed specimen is also reported from the Bertie Group (Přídolí) of New York, USA. Limuloides was revised as monospecific in the late 20th Century from a small sample of specimens, and there has been confusion regarding the assignment of English material to either Limuloides or sister genus Bunodes Eichwald, 1854, which is otherwise known from the Rootsiküla Formation or “Eurypterus dolomite” (Wenlock-Ludlow) of Saaremaa, Estonia. As such, the taxonomy, morphology, and stratigraphical distribution of Limuloides is circumscribed fully here based on fossils of over 50 bunodid individuals from seven collections, which are illustrated across 32 line-drawings and 46 photographs. Two Limuloides species are valid: the type species Limuloides limuloides (Woodward, 1865) and Limuloides horridus (Woodward, 1872a). All other species of Limuloides are characterised by features resulting from incomplete or atypical preservation and are shown to be junior synonyms of L. limuloides. The two valid species differ in the arrangement of the prosomal margin spines, the size and distribution of tubercles on the prosoma, and the shape of the prosoma. L. horridus is known from only a single prosoma from the Wenlock of Dudley, West Midlands. L. limuloides is known from two Wenlock prosomae, one from Dudley and one from Ledbury, Herefordshire, in addition to numerous younger specimens including four opisthosomae. The most well preserved, numerous and stratigraphically constrained L. limuloides specimens are from the channel-fill deposits of Leintwardine, Herefordshire (Saetograptus leintwardinensis Zone, lower Ludfordian); these reveal the complete dorsal exoskeleton, a small pair of median ocelli and the absence of lateral compound eyes. Further examples of Bunodidae from elsewhere in the English Ludlow and Přídolí are less well-preserved and often less precisely identifiable, assigned to L. limuloides, L. cf. limuloides and Bunodidae sp. Some assigned to Bunodidae sp. bear close resemblance to Bunodes from Saaremaa but lack enough diagnostic features to be determined unequivocally. Bunodes was therefore likely present in the Anglo-Welsh basin but is absent from the key localities that have yielded unequivocal L. limuloides and L. horridus.